The present invention relates to a method of and means for manufacturing thin-walled hoses, and more particularly, to hoses made from synthetic plastic material, with a reinforcement which is strong relative to the wall thereof.
The trend as regards the development of hoses has recently been to manufacture very light and extremely flexible hoses having walls which are as thin as possible but which are strongly reinforced by a helical wire, such as those which are, for example, described in German Pat. No. 2,261,126.
It has so far been necessary for such hoses to be manufactured on production auxiliary mandrels, also known as support mandrels. This operational procedure has been necessary in order that the soft and sensitive hose core, at the time of applying the strong reinforcement, not be constricted or compressed under the prevailing coiling tension.
The commercial disadvantages as regards manufacture using auxiliary mandrels during production are serious. It is only possible to produce hoses of finite length, the limit of which at the present time may be in the region of 15 meters. However, industry requires greater lengths, for example, up to 100 to 150 meters. Another disadvantage as regards production on mandrels is apparent from German Offenlegungsschrift No. 2 608 94. It is clear from that disclosure the great expense necessary in order to make such a manufacture economic. Apart from the expense involved in such a manufacture, it is also necessary to take into account the area or space which is needed in respect of this installation.
An additional disadvantage with the manufacture on mandrels is the type of reinforcement which may possibly be applied. With hoses having opposite coils or turns, it is scarcely possible, or only with very great difficulty, for them to be freed from the auxiliary mandrels used during production. However, an oppositely directed reinforcement has the great advantage, as regards pressure loading of the hoses, that the said hoses are not distorted or twisted under the prevailing internal pressure. Radial reinforcements which extend in one direction yield under the prevailing internal pressure and thus lead to twisting or distortion of the hoses themselves, and this may, with loose hoses, lead to the formation of loops. This is a serious disadvantage, for example, with long hose pipes for compressed air. Furthermore, the conversion of such an installation to other hose diameters is very costly. Many devices have to be changed or replaced such as the drawing devices and devices for cutting to length, the storage arrangements and mandrels, etc.
It is known that hose cores having relatively thick walls are at the present time made, for example, with thin textile reinforcements, usually in the form of polyester filaments, without the use of support mandrels, as in shown from German Pat. No. 1 435 237, and that hoses which are coiled from strips and welded are occasionally produced, likewise without using production auxiliary mandrels.
However, when starting with thin-walled hose cores which are initially extruded axially, due to the fact that said cores at the present time mostly consist of synthetic thermoplastic material having a Shore hardness A of approximately 70, or of comparable equally soft rubber, it has not so far been possible thereafter to apply a strong reinforcement without the aid of support mandrels.
Previously, for example, with a finished hose having an external diameter of 15 mm and a reinforcement of polyethylene or hard PVC with a diameter of 1.5 mm, even in conjunction with the aforementioned measures of reducing the coiling tensions to a minimum, the limit of the formation without using auxiliary mandrels during production would be a hose core having a wall thickness of about 1.5 mm, which core must, however, be cooled beforehand to at least room temperature. This specific example only applies when the hoses are made with the modern improved coiling machines, which have electronically controlled winding drive units in addition to the main driving means, and not when other hose diameters are involved. In this case, it is always necessary to consider the relation between the reinforcement and the hose core which is to be reinforced.
Hoses, such as those which are, for example, described in the aforementioned German Pat. No. 2,261,126, generally require smaller wall thicknesses of their hose core and sheathing. Such a completed hose, with an external diameter of about 15 mm, is most advantageously given a hose core and sheathing with a thickness of only 0.5 mm, so as to function satisfactorily.
In the manufacture of hoses with coiled reinforcement, attempts have been made to reduce the coiling tension by using a guide means through which the hose is guided. The reinforcement is coiled upon the guide means in a manner so that the last turn coiled on the guide means will cause the first turn to be transferred to the hose and to be conveyed further by said hose, as shown, for instance, in DT-PS No. 1,435,257 and DT-OS No. 2,502,363. This manner of reducing the coiling tensions is, however, dependent on the tension in the reinforcing material as well as on the friction between said material and the guide means and the friction between adjacent turns on the guide means, which effects are adversely affected by a rotatable pusher element, as indicated in said DT-OS No. 2,502,363. The fact that the reinforcing material obtained from a respective bobbin will already be subject to variable tensions, constitutes one cause for variable friction forces on these guide means. Accordingly, by these known methods it is not possible to really obtain uniform coiled reinforcements.
It is an object of the present invention to provide a method and means for readily forming thin-walled hoses composed of a hose core of soft synthetic plastic under 0.5 mm thickness united with a strong reinforcement in the form of monofilaments and strips to several millimeters thickness without production auxiliary mandrels being required during the manufacturing process.